FIG. 1A schematically illustrates, in axial half section and in lateral perspective from above, a mold, denoted in its entirety by the reference 1, of a molding device at which the invention is aimed. The mold 1, having a longitudinal axis 7, comprises two mold halves 2A, 2B respectively, able to move one relative to the other, particularly in rotation (arrows 3A, 3B respectively) about a fixed common axle 4, and a mold base 5 which can move with respect to the two mold halves 2A, 2B in axial translation, as illustrated by the arrow 6, coaxial to the longitudinal axis 7 of the mold.
Each mold half 2A, 2B comprises a mold holder 8A, 8B respectively, which is equipped with respective support arms 15A, 15B articulated to said axle 4, a respective shell holder 9A, 9B, fixed to the corresponding mold holder in any way known to those skilled in the art and a respective shell 10A, 10B supported by the respective shell holder 9A, 9B in any way known to those skilled in the art. The two shells 10A, 10B and the mold base 5 comprise respective molding cavity portions 11A, 11B and 12 which, when the mold is in the closed position, together define a molding cavity 13 which is coaxial with the longitudinal axis 7 of the mold 1. A structure of this type is described and depicted for example in document FR-2 733 176.
Along the cooperating respective peripherals of the shells 10A, 10B and of the base 5, the shells are equipped with respective grooves 14A, 14B and the base is equipped with a radially projecting peripheral rib 29 able to be housed in the grooves 14A, 14B when the mold 1 is in the closed position as illustrated in FIG. 1A, so that the shells and the base form a mechanical assembly that is non-deformable in the presence of the blowing pressure (of the order of 40×105 Pa). Arrangements of this type are represented, for example, in documents FR-2 720 680, FR-2 828 829 and FR-2 841 495.
Finally, means 16 for compensating for the blow-molding pressure are provided between one of the mold holders 8A, for example, and the corresponding shell holder 9A, these pressure-compensating means 16 possibly in particular comprising a chamber between the mold holder 8A and the shell holder 9A as shown in FIG. 1A, it being possible for the chamber to be supplied with blow-molding fluid, during the blow-molding, by means that are not visible in FIG. 1A. An arrangement of this type may be found, for example, in document FR-2 659 265.
It will be noted that, in the depiction of FIG. 1A, the plane of section of the closed mold 1 is substantially diametral and substantially perpendicular to the parting line 17 of the shells 10A, 10B. It will also be noted that the shell holders 9A, 9B are slightly shorter around the periphery than the shells which means that, when the mold 1 is closed, there remains a gap 18 between their facing respective longitudinal edges so as to ensure that the shells bear correctly against one another along the parting line 17.
In the configuration illustrated in FIG. 1A, the shells 10A, 10B have a height substantially equal to that of the respective shell holders 9A, 9B, which is the height of the mold 1. Thus, the molding cavity 13 has the maximum permissible height for this mold and corresponds to the maximum height of the containers that can be manufactured using this mold.
In order to improve the production capability of the mold, it is desirable for it to be able to be configured for manufacturing not only said maximum-height containers, but also for manufacturing containers of lesser heights. To these ends, it is known practice for the shells 10A, 10B equipped with the respective molding cavity portions 11A, 11B, to be replaced by shells 20A, 20B equipped with different molding cavity portions 19A, 19B, (in this instance, molding cavity portions that are not as tall) as shown in FIG. 1B. In practice, the shells 20A, 20B are positioned at the top of the shell holders so that their respective upper faces remain at the same level as the respective upper faces of the shell holders so that there is no need to alter the layout of the other functional elements needed for blow-molding or stretch-blow-molding the container. The cavity portions 19A and 19B and the cavity portion 12 in the base together, when the mold is in the closed position, define a molding cavity 21 that is not as tall as the molding cavity 13 of FIG. 1A. Thus the overall arrangement of the molding device is maintained, with the mold holders 8A, 8B and the shell holders 9A, 9B, and the base 5 the axial position of which needs to be modified in relation to the reduction in height of the molding cavity portions.
In this known solution, the shells 20A, 20B equipped with the shorter-height molding cavity portions 19A, 19B maintain the same height as the shells 10A, 10B of FIG. 1A. In this case, the lower parts 22A, 22B of the shells 20A, 20B, situated below the base 5—that is to say below the grooves 14A, 14B respectively—are in the form of simple semi-cylindrical walls of revolution as is clearly visible in FIG. 1B. These lower parts 22A, 22B thus constitute integral parts of the respective shells 20A, 20B to which they belong and are of one piece with the upper parts of the shells that comprise the respective cavity portions 19A, 19B respectively.
The advantage of the conventional structure that has just been explained lies in the fact that, when the mold is in the closed position, the two shells 20A, 20B bear against one another along the parting line 17, even in the bottom of the mold. In other words, the two lower parts 22A, 22B together form a cylindrical annular support of revolution against which the two shell holders 9A, 9B respectively can bear when the chamber that forms part of the pressure-compensating means 16 is subjected to the blow-molding pressure. An annular support such as this thus opposes radial deformation, towards the center, of the lower part of the shell holder 9A to which the blow-molding pressure is applied.
However, this known structure does at the same time have the appreciable disadvantage that the shells 20A, 20B are machined from solid, which, when machining the lower parts 22A, 22B, entails removing a significant volume of material. This results in waste materials, machining time, and therefore results in height costs.